The fragmenting potworm Enchytraeus japonensis (Oligochaeta, Annelida) reproduces asexually by dividing the body into several fragments that then regenerate to complete individuals in 4-5 days. Such large-scale regeneration, however, occurs only in some invertebrates. To better our understanding of why regeneration is so limited in many animals, despite their ability to undergo embryonic development from the single cell of a fertilized egg, comparisons were made between regeneration and embryonic development of E. japonensis by using two methods: histochemistry for alkaline phosphatase (ALP) and immunohistochemistry with an antibody against acetylated tubulin that visualizes nervous system development. The analyses revealed that both ALP expression patterns and central nervous system development differ between embryogenesis and the regeneration, suggesting that regeneration is not a simple reiteration of embryogenesis but involves different regulatory mechanisms. The study provides a basis for the elucidation of mechanisms that are unique and crucial to regeneration.